The systems and techniques described herein were made in the performance of work under a NASA contract, and are subject to the provisions of Public Law 96-517 (35 USC 202) in which the Contractor has elected to retain title.
This application relates to generation of oscillating signals by using opto-electronic oscillators.
Oscillating signals may be generated by using various types of oscillators having energy storage elements. The quality factor Q, or the energy storage time, of an energy storage element can determine the spectral linewidth of the respective oscillating signal. High quality factor Q or long energy storage time can be used to reduce the spectral linewidth of the oscillating signal and hence improve the signal spectral purity.
Spectrally pure oscillators in radio frequency (RF), microwave, and millimeter wave spectral ranges may be used for generating, tracking, cleaning, amplifying, distributing signal carriers, and other applications. Such signal carriers can be applied in communication, broadcasting, radar, measurements, and receiving systems in the radio frequency spectral range. Voltage-controlled RF oscillators with phase-locked loops can be used for, e.g., clock recovery, carrier recovery, signal modulation and demodulation, and frequency synthesizing.
The above signal oscillators can be constructed by opto-electronic oscillators (xe2x80x9cOEOsxe2x80x9d) having both electronic and optical components. See, e.g., U.S. Pat. Nos. 5,723,856 to Yao and Maleki and 5,777,778 to Yao. Such an OEO includes an electrically controllable optical modulator and at least one active opto-electronic feedback loop that comprises an optical part and an electrical part interconnected by an optical-to-electronic conversion unit such as a photodetector. The opto-electronic feedback loop receives the modulated optical output from the modulator and converts it into an electrical signal to control the modulator. The feedback loop produces a desired delay and feeds the electrical signal in phase to the modulator to generate and sustain both optical modulation and electrical oscillation in radio frequency spectrum when the total loop gain of the active opto-electronic loop and any other additional feedback loops exceeds the total loss.
OEOs use optical modulation to produce oscillations in frequency spectral ranges that are outside the optical spectrum, such as in RF and microwave frequencies. The generated oscillating signals are tunable in frequencies and can have narrow spectral linewidths and low phase noise in comparison with the signals produced by other RF and microwaves oscillators. Notably, the OEOs are optical and electronic hybrid devices. In particular, an OEO-generated oscillating signal can be carried by an optical carrier signal. Hence, OEOs can be used in optical communication devices and systems for various applications beyond the traditional use of the electronic RF oscillators.
A variety of OEOs can be constructed to achieve certain operating characteristics and advantages. For example, Coupled opto-electronic oscillators (xe2x80x9cCOEOsxe2x80x9d) described in U.S. Pat. No. 5,929,430 to Yao and Maleki can directly couple a laser oscillation in an optical feedback loop to an oscillation in an opto-electronic feedback loop. Opto-electronic oscillators can also be implemented by having a Brillouin optical medium in the optical portion of at least one active opto-electronic feedback loop to generate an electrical modulation signal based on the stimulated Brillouin scattering. U.S. Pat. No. 5,917,179 to Yao. Such a Brillouin OEO can use the natural narrow linewidth of the Brillouin scattering to select a single oscillating mode. Furthermore, the optical portion of each opto-electronic feedback loop may include an optical resonator to produce the desired delay. See, e.g., U.S. application Ser. No. 09/491,988 by Yao et. al. filed Jan. 26, 2000.
The present disclosure includes opto-electronic oscillators that implements a mechanism in the optical portion of an opto-electronic feedback loop to reduce effects on operation of the OEOs caused by an acceleration of the OEOs in motion.